1. Field of the Invention
The present invention relates to a method of and apparatus for forming a thin film through ion impact, and to circuit devices having such a thin film. The invention is particularly suitable for application to barrier layers or wiring films of large scale integrated circuits.
2. Description of the Prior Art
As the density of integration in large scale integrated circuits (LSIs) or very large scale integrated circuits (VLSIs) becomes high, the diameters of contact holes between a silicon substrate and an aluminum wiring film and of through holes between aluminum wiring layers become small, resulting in a larger aspect ratio as shown in FIG. 21. With a magnetron sputter method commonly used in the art, as the aspect ratio becomes near 1, the step coverage shown in FIG. 21 becomes poor due to the shadowing effect during sputter deposition of wiring material, so that wiring failure due to an increase in wiring resistance or electromigration may occur. To eliminate such disadvantages, a bias sputter method, as disclosed in Japanese Patent Unexamined Publication JP-A-61-261472 (corresponding to EP-A-202572) and Japanese Patent Unexamined Publication JP-A-61-214174 (no corresponding foreign application), has been developed whereby a film is formed while applying negative voltages to a target and a substrate at all times. The principle of a DC magnetron bias sputter method is exemplarily shown in FIG. 16. A sputter DC power source 12 is connected to a target 6, while a bias (reverse sputter) DC power source 11 is connected to a substrate 8. These negative electrodes are always supplied with DC negative voltages as shown in FIG. 17 during film formation so that a film is formed while the substrate 8 is being subjected to Ar ion impact (reverse sputter). Therefore, the step coverage is improved as compared with the sputter method employing no bias voltage. In FIG. 16, reference numeral 7 denotes magnets, 10 insulators, 17 a vacuum chamber.
However, it has been found that the crystal orientation (111) of an aluminum wiring film formed by the bias sputter method becomes considerably degraded. It is known that the orientation of crystalline grains is related to electromigration and stressmigration, and the more the orientation becomes excellent, the more the tolerance against electromigration and stressmigration is improved. It has also been found that the bias sputter method may cause cracks in a barrier layer and an inferior barrier effect.